Conventionally, in the field of vehicle lighting unit, vehicle headlights have been suggested which include a semiconductor laser element employed as a light source (for example, see Japanese Patent No. 5122542 or its corresponding U.S. Patent Application Laid-Open Publication No. 2011-063115A1, hereinafter referred to as Patent Literature 1).
FIG. 1 is a longitudinal sectional view illustrating a vehicle headlight 200 disclosed in Patent Literature 1.
As illustrated in FIG. 1, the vehicle headlight 200 disclosed in Patent Literature 1 can include: a semiconductor laser element 210 serving as a laser light source; a phosphor 220 to be irradiated with a laser beam lased by the semiconductor laser element 210; a reflector 230; a retainer member 240 for retaining the phosphor 220; and a light detector 250 (which is made up of an optical filter 252 serving to shield light at a predetermined wavelength and a light-receiving element 254). The optical filter 252 to be used can shield light having a converted wavelength (visible light) and transmit laser light.
The vehicle headlight 200 constructed as mentioned above can be configured such that the phosphor 220 is determined to have become chipped due to some cause when the intensity of light detected on the light-receiving element 254 (the value of a current flowing through the light-receiving element 254) is equal to or greater than a predetermined value (threshold value), and then the operation of the semiconductor laser element 210 is stopped.
However, the vehicle headlight 200 constructed as mentioned above has the problem of an increase in size because the light detector 250 is disposed outside the front end of the reflector 230 and on a line L1 extending through the phosphor 220 from a line connecting between the semiconductor laser element 210 and the phosphor 220.